@gianni333, i don't know how big difference that makes, but i have no doubts, that by including native format you would increase your chances to sell. Of course that largely depends on what your native format is. Max scene would draw a lot more attention than blend file.
I did an experiment a year ago, i've put one of my most popular free models in as many formats as i could and after some time i calculated how many times each format was downloaded. Needless to say that native formats was much more populare than interchangable ones. Oddly enough FBX wasn't much popular even compared against interchangable formats. You can see results of that experiment here: https://www.cgtrader.com/forum/topics/most-popular-file-formats